Shadow mask frame with curved supporting flange paralleling screen surface



July 25, 1967 R. c. DEMMY 3,333,134

SHADOW MASK FRAME WITH CURVED SUPPORTING FLANGE PARALLELING SCREEN SURFACE Filed June 122 196 2 Sheets-$heet 1 INVENTOR July 25, 1967 R. c. DEMMY 3,333,134

SHADOW MASK FRAME WITH CURVED SUPPORTING FLANGE PARALLELING SCREEN SURFACE Filed June 12, 1964 2 Sheets-Sheet INVENTOR /Foazfir C flaw/Mr val a ,4 omer/ United States Patent SHADOW MASK FRAME WITH CURVED SUP- PORTING FLANGE PARALLELING SCREEN SURFACE Robert C. Demmy, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Filed June 12, 1964, Ser. No. 374,588 1 Claim. (Cl. 31385) This invention relates to shadow mask color cathode ray tubes and particularly to the shadow mask electrode thereof and a method of fabricating the electrode. I

Shadow mask cathode ray tubes usually comprise a mosaic screen of phosphor dots, electron gun means for exciting the screen, and a shadow mask electrode interposed between the gun and screen. The shadow mask electrode usually includes a thin, multi-apertured sheet of metal disposed adjacent to, coextensive with, and substantially parallel to the mosaic screen, with the apertures thereof positioned in a systematic relationship with dots of the screen.

In herein describing a mask electrode as being parallel to the phosphor screen, it is not intended to exclude a mask-screen spacing relationship which varies from parallelism by a controlled amount for the purpose of obtaining a desired register of the electron beams on the phosphor dots.

In one form of shadow mask cathode ray tube, the mosaic screen and the shadow mask electrode are generally rectangular with rounded corners and outwardly bowed sides. The major surfaces of the screen and mask electrode are curved, e.g., approximately spherically curved. For the sake of brevity, such a mosaic screen and shadow mask electrode will hereinafter be referred to simply as rectangular and curved, or domed.

One form of prior art rectangular, domed shadow mask electrode is of the one-piece type. Such an electrode comprises a thin metal sheet whose central portion is domed and multi-apertured and whose peripheral portion is shaped to provide a somewhat stiffened rim section.

Another form of prior art rectangular, domed shadow mask electrode comprises a domed, multi-apertured, thin metal sheet mounted across a considerably heavier rectangular frame. The frame is formed by a deep-drawing process. The frame has an L-shaped cross-section with two flanges perpendicular to each other. One flange of the L extends toward the screenand has its edge contoured to generally conform thereto. The other flange of the L is substantially planar. Consequently, the width of the contoured flange varies along the length of the frame, thus giving the frame a non-uniform cross-section.

Both the'one-piece mask electrode and the prior art two-piece mask electrode with the deep-drawn, variable cross-section frame are subject to undesirable dimensional changes due to heating caused by electron bombardment. The one-piece electrode, because of its small mass, exhibits a fluctuating distortion during operation of the tube when the displayed image changes back and forth between a dark scene to a light scene. The prior art two-piece mask electrode, although relatively free from such temperature fluctuations, becomes substantially distorted to an equilibrium during the operation because of the non-uniformity of the frame cross-section. This distortion, in turn, results in a distortion of the multi-apertured sheet metal masking member. Either type of distortion may adversely affect the color purity of the image displayed on the screen. Furthermore, the one-piece mask electrode, because of its small mass and thin-section rim, has insuificient mechanical rigidity if, in accordance with preferred practices, it is detachably mounted on a plurality of studs fixed to the Patented July 25, 1967 "ice tube envelope to permit quick removal of the mask electrode during manufacture.

It is an object of this invention to provide a domed, rectangular shadow mask electrode which, compared to prior art mask electrodes of this type, exhibits either or both improved mechanical rigidity and reduced dimen sional changes due to bombardment by an electron beam.

In a shadow mask cathode ray tube having a domed, rectangular phosphor screen, a shadow mask electrode according to the invention comprises a rectangular frame of relatively thick material and a relatively thin multiapertured sheet metal masking member mounted thereacross. The frame has an approximately L-shaped crosssection whose shape and size are substantially uniform along the length of the frame. The four sides of the rectangular frame are curved so that they are substantially parallel to the phosphor screen. The multi-apertured, sheet metal masking member is domed to also generally conform to the curvature of the screen.

In the drawings:

FIG. 1 is a longitudinal view partially in section of a shadow mask color cathode ray tube embodying the invention;

FIG. 2 is a plan view of the shadow mask electrode of the tube of FIG. 1 with a part broken away; and

FIGS. 3 and 4 are sections taken respectively along lines 3--3 and 44 of FIG. 2.

Referring to the drawings, a cathode ray tube 10 includes an envelope 12 having a central longitudinal axis A-A. The envelope 12 comprises a shallow bowl-like faceplate panel 14 sealed by a frit seal 18 at its open end to a mating open end of a funnel member 16. The faceplate panel 14 comprises a rectangular, domed, faceplate 20 and a peripheral side-wall 22.

A domed, rectangular mosaic luminescent screen 26 comprising a multiplicity of elemental dot-like deposits of different color-emitting phosphors is disposed on the internal surface of the faceplate 20. The screen 26 may be aluminized according to known techniques.

A shadow mask electrode 28 is disposed adjacent to, substantially co-extensive with, and approximately parallel to the mosaic phosphor screen 26. The shadow mask electrode 28 comprises a domed, rectangular multi-apertured sheet metal masking member 30 mounted across a rectangular frame 32.

A plurality of (e.g., four) electrode support studs36 extend from the internal surface of the panel side-wall 22 at locations nearly midway between the four corners thereof.

A- plurality of leaf spring support straps 40 are fixed at their one ends to the shadow mask electrode frame 32. The support straps 40 are provided with suitable apertures near their other (free) ends into which the support studs 36 are received so as to provide a detachable, readily removable and replaceable shadow mask electrode 28 within the panel 14. The spring support straps 40 are such that their apertured free ends may be depressed toward the frame 32 to permit the shadow mask electrode 28 to be mounted onto or removed from the studs 36. Such mounting of the mask electrode 28 is useful to permit quick removal and remounting of the mask electrode 28 during the manufacture of the mosaic phosphor screen 26 in accordance with known screening practices.

An electron gun assembly 42 is disposed Within the neck portion of the funnel member 16. The gun assembly 42 is adapted to project a plurality of electron beams through the apertures of the masking member 30 and onto the mosaic phosphor screen 26.

The frame 32 comprises an endless strip of metal formed in a generally rectangular shape having two long side lengths 44 and two short side lengths 46. The strip has a generally L-shaped cross-section which is of substantially uniform size along the strip. The L is oriented with a transverse flange 48 extending inwardly toward the axis AA from the rear edge of an axial flange 50 extending toward the screen 26.

The cross-sectional uniformity of the frame 32 results in more uniform thermal expansion characteristics than exhibited by prior art deep-drawn, variable cross-section frames. Accordingly, with the frame 32 there is less undesirable distortion of the masking member 30 than is the case with prior art deep-drawn frames.

Each of the four sides of the rectangular frame 32 is bowed both outwardly (FIG. 2) away from the central longitudinal axis AA of the tube and along (FIGS. 3 and 4) the axis AA toward the phosphor screen 26. The bow of the four sides 44 and 46 of the rectangular frame is such as to dispose the forward (distal, or remote from the gun) edge 51 of the axial flange 50 substantially parallel to the phosphor screen 26, i.e., the curvature of the frame sides 44 and 46' conform generally to that of the faceplate 20. Because of the bow of the frame sides 44 and 46, the transverse flange 48 is non-planar. Preferably, the transverse flange 48 is formed at an acute angle 0 to Y the axial flange 50 so that the flange 48 is approximately parallel, that is its major surfaces are parallel, to the phosphor screen 26.

One advantage which results from the transverse flange 48 being substantially parallel to'the phosphor screen 26 rather than perpendicular to the axis AA is improved electron beam shadowing of the inner surface 52 of the axial flange 50. One function of the transverse flange 48 is to shadow the inner surface 52 of the axial flange 48 from electrons which would otherwise strike the inner surface 52, be deflected therefrom, pass through the apertures of the masking member 30 and produce undesirable screen excitation. By making the transverse flange 48 parallel to the phosphor screen 26, and thereby more nearly perpendicular to the electron beam path, the flange need not be as wide to completely shadow the axial flange 48 as it would have to be if it were perpendicular to the axis AA. Accordingly, the transverse flange enables the provision of a lighter weight frame 32 and an attendant cost saving on material.

The frame 32 is of considerably thicker material than the masking member 30. It may be as much as about or more times as thick. For example, in one embodiment of the shadow mask electrode 28, the frame has been made of 0.093 inch thick material whereas the masking member has been made of 0.006 inch thick material. A relatively thin masking member 30 is very desirable from a practical standpoint because it minimizes electron interception by the side walls of the apertures therein. The provision of a relatively thick, massive frame is highly desirable so as to provide a good heat sink to stabilize the operational temperature of the shadow mask electrode 28 and prevent temperature fluctuations and .attendant dimensional fluctuations of the thin masking member 30.

Although some prior art two-piece mask electrodes have had relatively massive frames they did not have uniform cross-sections because of the conventional prior art process used to fabricate them, viz., a deep-drawing process. Furthermore, because of the deep-drawing process used, such prior art frames had a planar transverse flange rather than the more desirable curved transverse flange parallel to the phosphor screen.

According to prior art shadow mask electrode design and fabrication techniques, it has not been possible to obtain the combined advantages of: (a) a relatively massive frame, (b) a uniform frame cross-section, and (c) a curved transverse flange parallel to the phosphor screen.

The frame 32 with these combined advantages can be spherical surface to desirably shape it to accept the domed masking member 30. This fabrication method automatically provides the desired parallel relationship between the transverse flange 48 and the phosphor screen 26.

What is claimed is: A cathode ray tube comprising: an envelope including a rectangular faceplate having a substantially spherical concave internal surface disposed perpendicularly to a central tube axis, a mosaic phosphor screen disposed on said surface, electron gun means for projecting electrons onto said screen, and a a domed, rectangularshadow mask electrode disposed between said screen and said gun means,

said electrode comprising a rectangular frame and a rectangular multi-apertured sheet metal masking member mounted across said frame, said frame comprising an endless strip of metal having a substantially uniform L-shaped cross-section,

one of the flanges of the L having its major faces spherically curved and disposed substantially parallel to said concave faceplate surface,

the other of the flanges of said L extending substantially parallel to said axis toward said screen from the' i outer periphery of said one flange, said multi-apertured masking member being curved with a convex surface thereof facing said concave faceplate surface and being attached to the screen edge of said other flange,

said flanges having a thickness many times the thickness of said multi-apertured masking member and a plurality of mask mounting means connected between said other flange and said faceplate adjacent to said spherical internal surface.

References Cited UNITED STATES PATENTS 9/1957 McQuillen et al 31392.5 7/1959 Fiore -313- X 9/ 1959 Woughter et al 313-89 X 1/1960 Haas 313-85 11/1960 Fyler 313--64 OTHER REFERENCES Fink: Television Engineering Handbook, McGraw-Hill Book Co., Inc'., New York, 1957, pages 5-1054.

JAMES W. LAWRENCE, Primary Examiner. ROBERT SEGAL, Examiner. 

